docs: added AWS WorkMail hello world app in examples (#670)

examples/2016-10-31/workmail-hello-world-python/README.md

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+# AWS WorkMail hello world
+
+This is a hello world example of the WorkMail lambda feature. For more information see [AWS WorMail lambda documentation](https://docs.aws.amazon.com/workmail/latest/adminguide/lambda.html)
+
+To use this application you can deploy it via Lambda console. Visit [AWS Lambda Console](https://console.aws.amazon.com/lambda/home?region=us-east-1#/create?firstrun=true&tab=serverlessApps)
+
+### Local development
+
+First, [set up the SAM CLI](https://github.com/awslabs/aws-sam-cli/blob/develop/docs/installation.rst).
+
+Now, test the application locally using:
+
+`sam local invoke WorkMailHelloWorldFunction -e event.json`
+
+### Deploying
+
+```bash
+sam package \
+ --template-file template.yaml \
+ --output-template-file packaged.yaml \
+ --s3-bucket $YOUR_BUCKET_NAME
+```
+
+```bash
+sam deploy \
+ --template-file packaged.yaml \
+ --stack-name workmail-hello-world \
+ --capabilities CAPABILITY_IAM
+```
+
+### Configure WorkMail
+Find the ARN of your new lambda function using:
+
+```bash
+aws cloudformation describe-stacks \
+  --stack-name workmail-hello-world \
+  --query 'Stacks[].Outputs[0].OutputValue'
+```
+
+Now you can go to WorkMail console and configure an outbound rule to use your new lambda.
+

examples/2016-10-31/workmail-hello-world-python/event.json

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+{
+    "summaryVersion": "2018-10-10",
+    "envelope": {
+        "mailFrom" : {
+            "address" : "from@domain.test"
+        },
+        "recipients" : [
+           { "address" : "recipient1@domain.test" },
+           { "address" : "recipient2@domain.test" }
+        ]
+    },
+    "sender" : {
+        "address" :  "sender@domain.test"
+    },
+    "subject" : "Hello From Amazon WorkMail!",
+    "truncated": false
+}

examples/2016-10-31/workmail-hello-world-python/template.yaml

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+AWSTemplateFormatVersion: '2010-09-09'
+Transform: AWS::Serverless-2016-10-31
+Description: >
+    WorkMail hello world lambda SAM
+    
+Resources:
+    WorkMailHelloWorldFunction:
+        Type: AWS::Serverless::Function 
+        Properties:
+            CodeUri: workmail-hello-world/
+            Handler: app.lambda_handler
+            Runtime: python3.6
+            Timeout: 10
+
+    PermissionToCallLambdaAbove:
+        Type: AWS::Lambda::Permission
+        DependsOn: WorkMailHelloWorldFunction
+        Properties: 
+          Action: lambda:InvokeFunction
+          FunctionName: !Ref WorkMailHelloWorldFunction
+          Principal: !Sub 'workmail.${AWS::Region}.amazonaws.com'
+
+Outputs:
+      HelloWorldArn:
+              Value: !GetAtt WorkMailHelloWorldFunction.Arn

examples/2016-10-31/workmail-hello-world-python/workmail-hello-world/app.py

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+"""
+
+Hello world example for AWS WorkMail
+
+Parameters
+----------
+event: dict, required
+    AWS WorkMail Message Summary Input Format
+    For more information, see https://docs.aws.amazon.com/workmail/latest/adminguide/lambda.html  
+
+    {
+        "summaryVersion": "2018-10-10",                              # AWS WorkMail Message Summary Version
+        "envelope": {
+            "mailFrom" : {
+                "address" : "from@domain.test"                       # String containing from email address
+            },
+            "recipients" : [                                         # List of all recipient email addresses
+               { "address" : "recipient1@domain.test" },
+               { "address" : "recipient2@domain.test" }
+            ]
+        },
+        "sender" : {
+            "address" :  "sender@domain.test"                        # String containing sender email address
+        },
+        "subject" : "Hello From Amazon WorkMail!",                   # String containing email subject (Truncated to first 256 chars)"
+        "truncated": false                                           # boolean indicating if any field in message was truncated due to size limitations
+    }
+
+context: object, required
+    Lambda Context runtime methods and attributes
+
+    Attributes
+    ----------
+
+    context.aws_request_id: str
+         Lambda request ID
+    context.client_context: object
+         Additional context when invoked through AWS Mobile SDK
+    context.function_name: str
+         Lambda function name
+    context.function_version: str
+         Function version identifier
+    context.get_remaining_time_in_millis: function
+         Time in milliseconds before function times out
+    context.identity:
+         Cognito identity provider context when invoked through AWS Mobile SDK
+    context.invoked_function_arn: str
+         Function ARN
+    context.log_group_name: str
+         Cloudwatch Log group name
+    context.log_stream_name: str
+         Cloudwatch Log stream name
+    context.memory_limit_in_mb: int
+        Function memory
+
+        https://docs.aws.amazon.com/lambda/latest/dg/python-context-object.html
+
+Returns
+------
+Nothing
+"""
+def lambda_handler(event, context):
+    try:
+        fromAddress = event['envelope']['mailFrom']['address']
+        subject = event['subject']
+        print(f"Received Email from {fromAddress} with Subject {subject}")
+
+    except Exception as e:
+        # Send some context about this error to Lambda Logs
+        print(e)
+        raise e
+